Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$96.89	4.799%	$101.5398	$101.54	$101.55	$101.50
Purchase #2	$220.59	4.579%	$230.6908	$230.69	$230.70	$230.70
Purchase #3	$53.88	10.849%	$59.7254	$59.73	$59.75	$59.70
Purchase #4	$103.97	10.475%	$114.8609	$114.86	$114.85	$114.90
Purchase #5	$74.30	7.674%	$80.0018	$80.00	$80.00	$80.00
Purchase #6	$180.61	12.345%	$202.9063	$202.91	$202.90	$202.90
Purchase #7	$55.98	11.123%	$62.2067	$62.21	$62.20	$62.20
7 purchase totals =	$786.22		$851.9317	$851.94	$851.95	$851.90